Oxidation of carbonaceous materials in the presence of a non-alkaline medium to produce coal acids



y 1966 D. L. DECKER ETAL 3,259,650

OXIDATION OF CARBONACEOUS MATERIALS IN THE PRESENCE OF A NON-ALKALINEMEDIUM 'I'O PRODUCE COAL ACIDS Filed Nov. 12, 1963 1N VEN TORS.

l 0a//on L. Decker Rober/ M Mur/r/e A TTORNEYS United States Patent 3259 650 OXIDATION OF cARfioNAcEoUs MATERIALS IN THE PRESENCE OF ANON-ALKALINE MEDIUM T0 PRODUCE COAL ACIDS Dalton L. Decker and RobertMcMurtrie, Midland, Mich, assignors to The Dow Chemical Company,Midland, Mich., a corporation of Delaware Filed Nov. 12, 1963, Ser. No.333,248 6 Claims. (Cl. 260-515) This application is acontinu-ation-in-part of my copending application, Serial No. 5,307,filed January 28, 1960, and now abandoned.

The present invention relates to a method of making coal acids fromcarbonaceous materials and more particularly it concerns the productionof coal acids mixtures by thermal oxidation of said carbonaceousmaterials in an aqueous slurry.

Coal acids obtained as a product of the partial oxidation of acarbonaceous material are predominantly mixtures of polycarboxylicaromatic acids. They are usually classified into two broad groupsdesignated as the humic acids and water-soluble coal acids. The formerare high molecular weight alkaline-soluble, acid precipitable materialsbelieved to be intermediates in processes directed to the production ofthe lower molecular weight, water-soluble coal acids.

There are several known processes for the production of coal acids ofwhich the water-soluble coal acids are of primary interest. Thesemethods generally involve contacting a carbonaceous material at elevatedtemperatures with an oxidizing agent such as nitric acid, permanganatein an alkaline solution, or gaseous oxygen in an alkaline solution.These and other known processes employ large amounts of chemicalreagents relative to the amount of water-soluble coal acids produced.Also, after obtaining the reaction product mixture, it is usuallynecessary to add further amounts of reagents before separation of thecoal acids can be achieved.

It is, therefore, desirable, as an object of the present invention, toprovide a direct process for the production of coal acids mixturesobviating the need to employ large quantities of chemical reagents. Itis a further object of the present invention to provide a method wherebycarbonaceous materials can be converted to a large proportion ofwater-soluble coal acids in an aqueous medium. Other objects will becomeapparent hereinafter as the invention is more fully described.

In accordance With the present invention, coal acids mixtures can beprepared by a process which involves the step of contacting a vigorouslyagiated aqueous slurry of a carbonaceous material with gaseous oxygen atan elevated temperature for a sufiicient period of time to accomplishthe formation of coal acids.

In carrying out the invention an aqueous feed slurry is prepared by anyof a number of conventional methods. A carbonaceous feed material issubjected to grinding or other pulverizing treatment so as to provide afine, particulate materialwhich is easily dispersed in water. Thismaterial is supplied to a mixing vessel wherein it is dispersed in asufiicient quantity of water to provide the desired slurry concentratesubstantially free of alkaline materials. If desired, a small amount ofa viscosity-lowering agent may be added to the slurry to decreasepumping energy requirements. The prepared slurry is then pumped into apreheater wherein it is heated to a desirable pre-reaction temperature.

The preheated slurry of the carbonaceous material is introduced into asuitable gas-liquid phase reactor such as a mechanically stirred reactoror a turbulent flow reactor capable of maintaining vigorous agitation ofthe slurry. While therein the agitated slurry is contacted with gaseousoxygen at an elevated temperature for a suflicient period of time toaccomplish the formation of coal acids. Generally, a residence timewithin the reaction zone, from about 4 to 30 minutes, preferably about10 minutes, is. desirable. Residence time refers tothe period of timerequired for a particular portion of the slurry to pass through thereaction zone. By reaction zone is meant that portion of the reactor inwhich the agitated slurry is contacted with oxygen at an elevatedtemperature.

The reaction temperature can range from about 240 to about 320 C. with atemperature range from about 290 to about 300 C. being preferred. Sincethe oxidation reaction is exothermic, the necessary heat for maintainingthe reaction mixture at these temperatures is sup plied by the heat ofreaction.

To initiate the oxidation reaction of the present invention, it isnecessary to preheat the reactor feed slurrycontaining the carbonaceousmaterial to be oxidized to about 280 C. During subsequent continuousoperation, the preheat temperature is lowered to .a range from about 240to about 250 C.

Due to the importance of maintaining the reaction temperature within theaforementioned limits, it is generally desirable to provide coolingmeans for the reaction-zone. Cooling of the reaction zone can beconveniently accomplished by providing a jacketed reaction vessel orreaction tube in which moderate cooling fluids such as saturatedsteam-water mixtures can be applied to the vessel or tube outer walls.

Reaction pressures required within the reactor to maintain an aqueousliquid phase therein, as a minimum, cannot be less than the vaporpressure of steam over water :at the temperature of the reaction.Generally, over the reaction temperature range specified, the operatingpressure may range from about 900 to 1,800 pounds per square inchabsolute. The reaction can be carried out at substantially greaterpressures, but this has little elfect onthe elficiency of the conversionof the carbonaceous materials to coal acids. Usually it is preferred tooperate at pressures of from about 1,500 to 1,800 pounds per square inchabsolute.

I An operating variable of the present invention, which Is interrelatedwith the residence time of the reactants (oxygen and carbonaceousmaterial) within the reactor and the temperature maintained therein, isthe extent. of agitation of the reaction system. Vigorous agitation ofthe reaction mixture is critical for obtaining desirable yields of coalacids and such agitation must be maintained throughout the reactionzonein Order to obtain suitable heat and mass transfer rates. If the reactoris of the type that relies on turbulent flow within a pipeto accomplishthe desired state of agitation, Reynolds numbers Within the turbulentflow zone should be at. least about 20,000 and preferably about 75,000for elfective operation. Reynolds numbers within. mechanically stirredreactors Patented July 5, 1966 1 3 at the tip of the impeller should beat least about 100,000 for effective operation.

The product removed from the reaction zone substantially comprisesinsoluble unreacted carbonaceous materials, alkali-soluble andacid-precipitable humic acids, water-soluble coal acids, carbon dioxideand water. By virtue of the varying properties of its components, theeflluent product can be separated into its parts by meth ods well knownin the art such as precipitation, filtration, liquid-liquid extraction,leaching, fractionation and the like. The particular method orcombination of methods employed will depend upon the desired productseparation and purity required.

Generally, the product of prime interest is the watersoluble coal acidmixture which, as a mixture, predominantly comprises polyfunctionalpolycarboxylic aromatic acids having an average carboxylic acid groupfunctionality of about 2.5 to and an average equivalent weight based onthe carboxylic acid group functionality of about 75 to 90. This mixturecan be separated in toto as a mixture with a solvent such as methylethyl ketone or it can be separated by various means into its individualcomponents. 0. H. Grosskinsky et al., United States Letters Patent2,785,198, teaches a process for separating monocyclic aromaticpolycarboxylic acids from a crude oxidation product of carbonaceousmaterials.

In some instances of application, the efi'luent product of the processof the present invention comprising both humic acids and water-solublecoal acids is a desirable utile product in itself without furtherseparatory treatment. Such an admixture of coal acids is, for example,an effective additive for decreasing the viscosity of slurries such asdrilling muds for use in the petroleum industry.

The aqueous slurries employed in the present invention contain a finelyground or pulverized carbonaceous material in an amount from about 2percent to as much as 50 percent or more by weight of the total slurry.Preferably, the slurry contains from about 5 to percent by weight of thecarbonaceous material being oxidized. Slurries containing higher amountsof the carbonaceous material are oxidizable to coal acids but thepercent yield of such acids from a single pass within the reactor issubstantially decreased at higher slurry concentrations.

Carbonaceous materials suitable for oxidation by the method of thepresent invention for the production of coal acids include a variety ofcoals or other similar sources of condensed aromatic nuclei such as theanthracite coals, bituminous coals, lignites and the like, and includescarbonization products such as coke. By-product carbonaceous materialssuch as petroleum coke and charcoal are also operable. Moreparticularly, Reading anthracite, Pocahontas No. 3 low volatilebituminous, Harmon medium volatile bituminous, Sunnyhill No. 8 highvolatile bituminous and Island Creek high volatile bituminous areexemplary of coals which can be employed in the present invention toproduce coal acids.

Oxygen supplied to the reaction zone can be provided as in air orpreferably as a relatively pure component. Generally, amounts of oxygenemployed in the present invention to produce coal acids range from about1.5 to about 4.0 times the weight of the carbonaceous material employed.Lesser amounts of oxygen can be employed when less than the maximumconversion of the carbonaceous material to coal acids is desirable.

A representative process for the production of coal acids incorporatingthe present invention is shown schematically in the accompanyingdrawing.

A finely ground carbonaceous material 1 and water 2 are introduced intoa slurry feed tank 4 equipped with a mechanical mixer 5. Optionally aviscosity-lowering agent 3 may be introduced. The thoroughly mixedslurry is forced along a feed pipe line 10 by means of a positivedisplacement pump 6 into a preheater 8 operating on superheated steam.In order to alleviate pressure pulsations in the feed line 10, thelatter is connected to a surge tank 7. After leaving the preheater 8,the feed line discharges the slurry mixture directly into a multistagemechanically stirred reactor 16. Oxygen is supplied to the reactor fromoxygen storage 9 through an oxygen line 12 equipped with valve regulator13 responsive to a thermocouple 14 within the reaction zone of thereactor. The multistage reactor is equipped with a multiple turbinemixer 17 having turbine blades 11 mounted thereon which provide mixingfor each stage of the reactor. Individual cooling jackets 20 areprovided for four areas of the reaction Zone in order to accommodatevariances in cooling requirements. Stage dividers within the reactorvessel are fiat ring 'bafiles 21 and 27 with a center hole substantiallylarger than the mixer turbine drive shaft. Passage of materials fromstage to stage within the reactor is effected through these center holesin the bafiles. A safety discharge vent 18 and effluent product line 19are provided at the top of the reactor 16. The efiluent product line 19passes through a cooler 22 and thence to a receiving tank 23.

In a representative operation, a feed slurry containing 5 percent byweight of pulverized Pocahontas No. 3 coal (200 mesh) in water wasprepared in the mixing tank. This slurry was pumped by means of apositive displacement pump at a pressure of 1,500 pounds per square inchinto a three-gallon, nitrogen-filled, surge tank and thence into thepreheater comprising a 64 foot coil of inch I.D. tubing which is heatedby saturated steam contained in a surrounding steam jacket. Within thepreheater, the temperature of the slurry was increased to 270 C. for thestart-up period and to about 250 C. after continuous operationconditions had been achieved. From the preheater the feed slurry passedinto the bottom of the turbine-stirred reactor vessel at a rate of aboutpounds of slurry per hour which provided a residence time within thereactor vessel of about 10 minutes. The feed slurry was contacted withoxygen introduced at a rate of about 19 pounds per hour through anopening in the bottom of the turbine-stirred reactor. The oxygen supplywas regulated by means of a control valve device activated by athermocouple located within the reaction zone.

The slurry and oxygen passed concurrently through a series of ninestages within the reaction vessel. The reaction vessel, which had a 5inch inside diameter and a height of 5 feet, was divided into stages bymeans of a series of uniformly spaced fiat ring bafiles. Within eachstage, the feed slurry and oxygen were mixed by turbines rotating at 600r.p.m. providing Reynolds numbers of about 750,000. The pressure withinthe reaction vessel was maintained at about 1,500 pounds per square inchabsolute and the temperature ranged during the course of the reactionfrom about 280 to 300 C. During operation, the reactor was run full toprevent the accumulation of explosive gas mixtures.

The efiluent product taken from the top of the reactor was cooled andsubjected to separatory treatment to recover the water-soluble coalacids component. The crude product was first acidified with sulfuricacid to a pH of about 1. The insoluble unreacted coal residue andacidinsoluble humic acids were then allowed to settle out of the crudeproduct in a settling tank. Next, the water solution of the coal acidswas concentrated by evaporation and subsequently subjected toliquid-liquid extraction with methyl ethyl ketone. The methyl ethylketone extract was then evaporated to dryness leaving a residue whichwas a substantially pure mixture of water-soluble coal acids in a yieldof about 10 percent based on the total converted carbon.

Alternatively, the effluent product can be filtered to remove unreactedcoal and insoluble humic acids to thereby provide a water solution ofrelatively pure watersoluble coal acids. The water-soluble coal acidscan then be isolated as by evaporating such a solution to dryness.

Results of additional runs are tabulated below. These runs were carriedout in a similar manner to that of the foregoing run with the exceptionof certain variations in pressure, temperature and feed rates asindicated.

therewith, while maintaining the slurry at a temperature from about 240to about 320 C. and under autogenous pressure, contacting thenon-alkaline slurry with oxygen in an amount of from about 1.5 to about4.0 times the TABLE Pounds per Pound of Coal Input Coal Oxygen ReactorReactor Feed Feed Reactor Run Pressure, Temp, Rate, Rate, Efliuent,Waterp.s.i.a. C. lb./hr. lb./hr. lb./hr. Unreacted Hmmc Soluble MaterialAcids Coal Acids We claim: weight of carbonaceous material present for aperiod 1. A process for the production of coal acids which comprises thesteps of forming a non-alkaline, aqueous slurry containing from about 2to about 50 percent by weight of a finely divided carbonaceous material,vigorously agitating the slurry so as to achieve Reynolds numbers of atleast 20,000 therein and simultaneously therewith, while maintaining thetemperature of the slurry at a temperature Within the range from about240 to about 320 C., and under autogenous pressure, contact ing thenon-alkaline slurry with oxygen in an amount of from about 1.5 to about4.0 times the Weight of carbonaceous material present for a period oftime from about 4 to minutes, whereby coal acids are produced.

2. A process for the production of coal acids which comprises the stepsof heating a non-alkaline, aqueous slurry containing from about 2 toabout 50 percent by Weight of finely divided carbonaceous material up toa temperature of from about 240 to about 280 C., vigorously agitatingthe slurry so as to achieve Reynolds numbers of at least 20,000 thereinand simultaneously therewith, while maintaining the temperature of theslurry at a temperature within the range from about 240 to about 320 C.and under autogenous pressure, contacting the non-alkaline slurry withoxygen in an amount of from about 1.5 to about 4.0 times the weight ofcarbonaceous material present for a period of time from about 4 to 30minutes, whereby coal acids are produced.

3. A process for the production of coal acids which comprises the stepsof heating a non-alkaline, aqueous slurry containing from about 2 toabout 50 percent by weight of a finely divided carbonaceous material upto a temperature from about 240 to about 280 0.; passing the heatedslurry through a tube reactor at a rate such as to achieve Reynoldsnumbers of at least 20,000 therein and simultaneously therewith, whilemaintaining the slurry at a temperature from about 240 to about 320 C.and under autogenous pressure, contacting the non-alkaline slurry withoxygen in an amount of from about 1.5 to about 4.0 times the weight ofcarbonaceous material present for a period of time from about 4 to about30 minutes, whereby coal acids are produced.

4. A process for the production of coal acids which comprises the stepsof heating a non-alkaline aqueous slurry containing from about 2 toabout 50 percent by weight of a finely divided carbonaceous material upto a temperature from about 240 to about 280 C.; passing the heatedslurry through a turbine-stirred reaction zone wherein Reynolds numbersof at least about 100,000 at the tip of the impeller are maintained andsimultaneously of time from about 4 to about 30 minutes, whereby coalacids are produced.

5. A process for the production of coal acids which consists essentiallyof the steps of forming an aqueous slurry substantially free of alkalinematerials and containing from about 2 to about 50 percent by weight of afinely divided carbonaceous material, vigorously agitating the slurry soas to achieve Reynolds numbers of at least 20,000 therein andsimultaneously therewith, While maintaining the temperature of theslurry at a temperature within the range from about 240 to about 320 C.,and under autogenous pressure, contacting the slurry substantially freeof alkaline materials with oxygen in an amount of from about 1.5 toabout 4.0 times the weight of carbonaceous material present for a periodof time from about 4 to 30 minutes, whereby coal acids are produced.

6. A process for the production of coal acids which consists essentiallyof the steps of forming an aqueous slurry substantially free of alkalihydroxides and containing from about 2 to about 50 percent by weight ofa finely divided carbonaceous material, vigorously agitating the slurryso as to achieve Reynolds numbers of at least 20,000 therein andsimultaneously therewith, while maintaining the temperature of theslurry at a temperature within the range from about 240 to about 320 C.,and under autogenous pressure, contacting the slurry substantially freeof alkali hydroxides with oxygen in an amount of from about 1.5 to about4.0 times the weight of carbonaceous material present for a period oftime from about 4 to 30 minutes, whereby coal acids are produced.

References Cited by the Examiner UNITED STATES PATENTS 2,193,337 3/1940Leicester 260-528 2,461,740 2/ 1949 Kiebler 2605 15 2,786,074 3/1957Goren 260-514 OTHER REFERENCES Franke et al., Industrial and EngineeringChemistry,

1. A PROCESS FOR THE PRODUCTION OF COAL ACIDS WHICH COMPRISES THE STEPSOF FORMING A NON-ALKALINE, AQUEOUS SLURRY CONTAINING FROM ABOUT 2 TOABOUT 50 PERCENT BY WEIGHT OF A FINELY DIVIDED CARBONACEOUS MATERIAL,VIGOROUSLY AGITATING THE SLURRY SO AS TO ACHIEVE REYNOLDS NUMBERS OF ATLEAST 20,000 THEREIN AND SIMULTANEOUSLY THEREWITH, WHILE MAINTAINING THETEMPERATURE OF THE SLURRY AT A TEMPERATURE WITHIN THE RANGE FROM ABOUT240*TO ABOUT 320*C., AND UNDER AUTOGENOUS PRESSURE, CONTACTING THENON-ALKALINE SLURRY WITH OXYGEN IN AN AMOUNT OF FROM ABOUT 1.5 TO ABOUT4.0 TIMES THE WEIGHT OF CARBONACEOUS MATERIAL PRESENT FOR A PERIOD OFTIME FROM ABOUT 4 TO 30 MINUTES, WHEREBY COAL ACIDS ARE PRODUCED.